1. Field of the Invention
This invention relates to a method and an apparatus for reproducing program information from a medium in which noise generated by searching for predetermined program information on the medium is suppressed and, more particularly, to a disc player incorporating such a method and apparatus.
2. Description of the Prior Art
In a known recording system a rotatable disc-shaped record medium is used to record digital data representing an audio signal. The digital data are arranged in data blocks that include program information data representing the audio signal, data for error correction, synchronous data and address data. A disc player is used to reproduce the audio signal from the digital data recorded on the disc. With such a system, very high fidelity reproduction of the audio signal can be obtained.
However, errors in the program information data read by the disc player can affect the reproduced audio signal. Generally, digital data recorded in any medium inevitably contain data errors caused in the recording process. Such data error appear infrequently enough that a high fidelity audio signal can still be obtained from the program information data using error correction techniques. Fingerprints and scratches on the surface of the disc also can cause data errors because they prevent accurate reading of the program information data recorded on the disc.
Accordingly, recording and reproducing systems using digital data on a disc incorporate a cross-interleave error correction technique for correcting errors that appear in the program information data read from the disc. In recording data using a cross-interleave error correction technique, a first error correcting code for a first code arrangement stage and a second error correcting code for a second code arrangement stage are provided, and then an interleave is carried out between the first and second stages. Using a Reed-Solomon code for the error correcting codes and the interleave technique allows very accurate error correction of the reproduced program information data. However, the corresponding processing circuitry in the disc player for using that error correcting technique requires a finite time, called a de-interleave delay, to convert into program information the program information data read from the disc. That delay causes a problem.
The address data recorded on the disc with the program information data make it possible to reproduce selectively any desired portion of the program information data. The reading device in the disc player is made operative in a searching mode and address data contained in the output from the reading device is compared with designated address data associated with the location on the disc of the desired program information. The reading device is operated in the searching mode until the reproduced address data coincide with the designated address data. The reading device is then made operative in a playback mode to read the program information data at the location on the disc where the address data match the designated address data.
The output of the reading device in the searching mode also intermittently contains small amounts of program information data, which is supplied to the processing circuitry and converted into an audio signal after the de-interleave delay time. The audio signal thus obtained appears as a clicking noise or other undesired sound before the selected program information data is reached and converted into the desired program information. The de-interleave delay prevents suppression of that noise merely by preventing conversion of program information data into program information while the reading device is in the searching mode because the program information data in the output of the reading device can still be undergoing conversion after the searching mode is terminated.